An optical apparatus such as a pair of binoculars or a microscope is usually used for an observer to observe an object with his eye. Recently, there is proposed an optical apparatus having an image pickup function for recording an observed image. Such an optical apparatus has an imaging unit arranged in the main body of the apparatus.
Generally, a conventional binocular optical apparatus is structured such that the interpupillary adjustment is performed by rotating the left and right lens-barrels on the spindle. Further, in the case of an optical apparatus having an image pickup function, a visual field frame of an oblong rectangular or ellipsoidal shape corresponding to a shape of the image pickup device is displayed in the visual field, for discriminating between the observed image and the image pickup record area.
However, in the case where the interpupillary adjustment is performed is adjusted as described above, there is a problem that the visual field frame is inclined. Further, in the case where an imaging unit is arranged in the main body of a pair of binoculars, not only the visual field frame but also the imaging unit is inclined when the interpupillary adjustment is performed.
To solve the problems, have been considered a mechanism by which rotation of one lens-barrel makes the other lens-barrel rotate through the same degrees in the reverse direction to keep the imaging unit always horizontal in service condition, and a mechanism according to which the visual field frame is mounted rotatably about the optical axis of the optical system of a lens-barrel portion to correct the inclination of the visual field frame (See, for example, Japanese Non-examined Patent Laid-Open No. 2001-281555 (Patent Document 1)).